In many aviation applications, it is necessary to provide compressed air from the aircraft engines to the aircraft. The aircraft may utilize an auxiliary power unit (APU) to provide compressed air, both when the aircraft is on the ground and when it is in flight. Air can be taken from the APU to pressurize or to otherwise condition the cabin air, or for example, to cool avionics equipment or start the main engines on the ground or in-flight. In these aviation applications, there is a constant desire to improve performance and to decrease the size and weight.
A radial or centrifugal compressor can be used in the APU to compress air. In these cases, the compressor scroll is used to direct the compressed air from the centrifugal compressor and deliver it to aircraft ducting, which then carries it to various aircraft systems, such as the environmental control system (ECS) or the main engine starters. The compressor scroll is typically spiral-shaped with a radial opening that transitions through a body to an outlet. A number of considerations must be contemplated when designing the compressor scroll. Primarily, aerodynamic considerations must be weighed with sizing considerations. Typically, the compressor scroll should be able to redirect the compressed air from the inlet to the outlet while maintaining the quantity and uniformity of the velocity and pressure of the compressed air, as well as minimizing pressure drop. At the same time, it is advantageous to make the compressor scroll as compact as possible such that the overall size and weight of the APU can be minimized. Many conventional compressor scrolls require elongated or straight portions to prevent pressure loss and maintain the velocity, particularly at the outlet of the compressor scroll. However, these arrangements may compromise the size of the compressor scroll, and as a result, the overall size of the APU.
Accordingly, it is desirable to provide a more compact compressor scroll. In addition, it is desirable to provide a compressor scroll that maximizes performance while minimizing the size and weight of the compressor scroll. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.